Electrosurgical Devices With Choke Shorted to Biological Tissue

ABSTRACT

A device for directing energy to tissue includes a feedline and a radiating portion electrically coupled to the feedline. The radiating portion includes a distal radiating section and a proximal radiating section. The feedline includes an inner conductor, an outer conductor and a first dielectric material disposed therebetween. The device also includes a choke disposed around at least a portion of the feedline. The choke includes a second dielectric material disposed around at least a portion of the outer conductor, wherein the second dielectric material includes at least one opening defined therein, and an electrically-conductive member disposed in the at least one opening electrically coupled to the outer conductor, wherein the electrically-conductive member is configured to contact tissue.

BACKGROUND

1. Technical Field

The present disclosure relates to electrosurgical devices suitable foruse in tissue ablation applications and, more particularly, toelectrosurgical devices with a choke shorted to biological tissue andmethods of directing electromagnetic radiation to tissue using the same.

2. Discussion of Related Art

Treatment of certain diseases requires the destruction of malignanttissue growths, e.g., tumors. Electromagnetic radiation can be used toheat and destroy tumor cells. Treatment may involve inserting ablationprobes into tissues where cancerous tumors have been identified. Oncethe probes are positioned, electromagnetic energy is passed through theprobes into surrounding tissue.

In the treatment of diseases such as cancer, certain types of tumorcells have been found to denature at elevated temperatures that areslightly lower than temperatures normally injurious to healthy cells.Known treatment methods, such as hyperthermia therapy, heat diseasedcells to temperatures above 41° C. while maintaining adjacent healthycells below the temperature at which irreversible cell destructionoccurs. These methods involve applying electromagnetic radiation toheat, ablate and/or coagulate tissue. Microwave energy is sometimesutilized to perform these methods. Other procedures utilizingelectromagnetic radiation to heat tissue also include coagulation,cutting and/or ablation of tissue.

Electrosurgical devices utilizing electromagnetic radiation have beendeveloped for a variety of uses and applications. A number of devicesare available that can be used to provide high bursts of energy forshort periods of time to achieve cutting and coagulative effects onvarious tissues. There are a number of different types of apparatus thatcan be used to perform ablation procedures. Typically, microwaveapparatus for use in ablation procedures include a microwave generatorthat functions as an energy source, and a microwave surgical instrument(e.g., microwave ablation probe) having an antenna assembly fordirecting the energy to the target tissue. The microwave generator andsurgical instrument are typically operatively coupled by a cableassembly having a plurality of conductors for transmitting microwaveenergy from the generator to the instrument, and for communicatingcontrol, feedback and identification signals between the instrument andthe generator.

There are several types of microwave probes in use, e.g., monopole,dipole and helical, which may be used in tissue ablation applications.In monopole and dipole antenna assemblies, microwave energy generallyradiates perpendicularly away from the axis of the conductor. Monopoleantenna assemblies typically include a single, elongated conductor. Atypical dipole antenna assembly includes two elongated conductors thatare linearly aligned and positioned end-to-end relative to one anotherwith an electrical insulator placed therebetween. Helical antennaassemblies include helically-shaped conductor configurations of variousand dimensions, e.g., diameter and length. The main modes of operationof a helical antenna assembly are normal mode (broadside), in which thefield radiated by the helix is maximum in a perpendicular plane to thehelix axis, and axial mode (end fire), in which maximum radiation isalong the helix axis.

A microwave transmission line typically includes a long, thin innerconductor that extends along the longitudinal axis of the transmissionline and is surrounded by a dielectric material and is furthersurrounded by an outer conductor around the dielectric material suchthat the outer conductor also extends along the transmission line axis.In one variation of an antenna, a waveguiding structure, such as alength of transmission line or coaxial cable, is provided with aplurality of openings through which energy “leaks” or radiates away fromthe guiding structure. This type of construction is typically referredto as a “leaky coaxial” or “leaky wave” antenna.

During certain procedures, it can be difficult to assess the extent towhich the microwave energy will radiate into the surrounding tissue,making it difficult to determine the area or volume of surroundingtissue that will be ablated.

SUMMARY

The present disclosure relates to a device for directing energy totissue including a feedline and a radiating portion electrically coupledto the feedline. The radiating portion includes a distal radiatingsection and a proximal radiating section. The feedline includes an innerconductor, an outer conductor and a first dielectric material disposedtherebetween. The device also includes a choke disposed around at leasta portion of the feedline. The choke includes a second dielectricmaterial disposed around at least a portion of the outer conductor,wherein the second dielectric material includes one or more openingsdefined therein, and an electrically-conductive member disposed in theone opening(s) electrically coupled to the outer conductor, wherein theelectrically-conductive member is configured to contact tissue.

The present disclosure also relates to ablation probe for providingenergy to tissue including an inner conductor, an outer conductorcoaxially surrounding the inner conductor, the outer conductor having aproximal portion and a distal portion. A first dielectric material isdisposed between the inner conductor and the outer conductor, and asecond dielectric material disposed around at least a portion of thedistal portion of the outer conductor. The ablation probe also includesa third dielectric material disposed around the proximal portion of theouter conductor, wherein the third dielectric material includes anopening defined therein. An electrically-conductive member is disposedin the opening electrically coupled to the proximal portion of the outerconductor, wherein the electrically-conductive member is configured tocontact tissue.

The present disclosure also relates to a method of directing energy totissue that includes the initial step of positioning an antenna assemblyfor delivery of energy to tissue. The antenna assembly includes aradiating portion, a feed point, and a choke electrically coupleable totissue, wherein the choke is spaced apart from and disposed proximal tothe feed point. The method also includes the steps of transmittingenergy from an energy source to the antenna assembly, and causing theenergy to radiate through the radiating portion to tissue while shortingthe choke to tissue for blocking propagation of reflected energy towardsthe energy source.

BRIEF DESCRIPTION OF THE DRAWINGS

Objects and features of the presently disclosed antenna assemblies willbecome apparent to those of ordinary skill in the art when descriptionsof various embodiments thereof are read with reference to theaccompanying drawings, of which:

FIG. 1 is a schematic diagram of an ablation system in accordance withan embodiment of the present disclosure;

FIG. 2A is a partial, longitudinal cross-sectional view of an embodimentof the energy applicator of the ablation system shown in FIG. 1 inaccordance with the present disclosure;

FIG. 2B is a partial, longitudinal cross-sectional view of anotherembodiment of the energy applicator of the ablation system shown in FIG.1 in accordance with the present disclosure;

FIG. 3 is an enlarged view of the indicated area of detail of FIG. 2B,showing the junction member disposed between the proximal and distalradiating portions, in accordance with the present disclosure;

FIG. 4A is an enlarged view of the indicated area of detail of FIG. 2A,showing the electrically-conductive member, in accordance with thepresent disclosure;

FIG. 4B is a cross-sectional view of another embodiment of theelectrically-conductive member of FIG. 2A in accordance with the presentdisclosure;

FIG. 5 is a partial, perspective view of another embodiment of an energyapplicator in accordance with the present disclosure shown with indiciagraduation marks and an indicia alignment mark;

FIG. 6 is a diagrammatic representation of a radiation pattern ofelectromagnetic energy delivered into tissue by an energy applicator,such as the energy applicator of FIG. 5, in accordance with the presentdisclosure;

FIG. 7 is a cross-sectional view of an embodiment of an energyapplicator shown with a diagrammatic representation of an emittedradiation pattern in accordance with the present disclosure;

FIG. 8 is a graph showing simulation results for an embodiment of anenergy applicator in accordance with the present disclosure;

FIG. 9 is a graph showing simulation results for another embodiment ofan energy applicator in accordance with the present disclosure; and

FIG. 10 is a flowchart illustrating a method of directing energy totissue in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION

Hereinafter, embodiments of the presently disclosed electrosurgicaldevices will be described with reference to the accompanying drawings.Like reference numerals may refer to similar or identical elementsthroughout the description of the figures. As shown in the drawings andas used in this description, and as is traditional when referring torelative positioning on an object, the term “proximal” refers to thatportion of the apparatus that is closer to the user and the term“distal” refers to that portion of the apparatus that is farther fromthe user.

Electromagnetic energy is generally classified by increasing energy ordecreasing wavelength into radio waves, microwaves, infrared, visiblelight, ultraviolet, X-rays and gamma-rays. As it is used in thisdescription, “microwave” generally refers to electromagnetic waves inthe frequency range of 300 megahertz (MHz) (3×10⁸ cycles/second) to 300gigahertz (GHz) (3×10¹¹ cycles/second). As it is used in thisdescription, “ablation procedure” generally refers to any ablationprocedure, such as microwave ablation, radio frequency (RF) ablation ormicrowave ablation assisted resection. As it is used in thisdescription, “transmission line” generally refers to any transmissionmedium that can be used for the propagation of signals from one point toanother.

Various embodiments of the present disclosure provide electrosurgicaldevices for treating tissue and methods of directing electromagneticradiation to a target volume of tissue. Embodiments may be implementedusing electromagnetic radiation at microwave frequencies or at otherfrequencies. An electrosurgical system including an energy applicator,according to various embodiments, is designed and configured to operatebetween about 500 MHz and about 10 GHz with a directional radiationpattern.

Various embodiments of the presently disclosed electrosurgical devicesare suitable for microwave ablation and for use to pre-coagulate tissuefor microwave ablation assisted surgical resection. Although variousmethods described hereinbelow are targeted toward microwave ablation andthe complete destruction of target tissue, it is to be understood thatmethods for directing electromagnetic radiation may be used with othertherapies in which the target tissue is partially destroyed or damaged,such as, for example, to prevent the conduction of electrical impulseswithin heart tissue. In addition, although the following descriptiondescribes the use of a dipole microwave antenna, the teachings of thepresent disclosure may also apply to a monopole, helical, or othersuitable type of microwave antenna.

Various embodiments of the presently disclosed electrosurgical devicesinclude an antenna assembly and a feedline having an inner and outerconductor for supplying signals to the antenna assembly, wherein thefeedline and/or antenna assembly is provided with anelectrically-conductive member (e.g., 295 shown in FIG. 2A) electricallycoupled to the outer conductor (e.g., 260 shown in FIG. 2A), wherein theelectrically-conductive member is configured to make contact with tissue(e.g., “T” shown in FIG. 6) during a procedure, e.g., an ablationprocedure.

FIG. 1 shows an electrosurgical system 10, according to an embodiment ofthe present disclosure that includes an energy applicator or probe 100.Probe 100 generally includes an antenna assembly 12 having a radiatingportion connected by a feedline 110 (or shaft) via a transmission line15 to a connector 16, which may further operably connect the probe 100to an electrosurgical power generating source 28, e.g., a microwave orRF electrosurgical generator.

Feedline 110 may be formed from a suitable flexible, semi-rigid or rigidmicrowave conductive cable and may connect directly to anelectrosurgical power generating source 28. Alternatively, the feedline110 may electrically connect the antenna assembly 12 via thetransmission line 15 to the electrosurgical power generating source 28.Feedline 110 may have a variable length from a proximal end of theantenna assembly 12 to a distal end of transmission line 15 ranging froma length of about one inch to about twelve inches. Feedline 110 may beformed of suitable electrically-conductive materials, e.g., copper,gold, silver or other conductive metals or metal alloys having similarconductivity values. Feedline 110 may be made of stainless steel, whichgenerally offers the strength required to puncture tissue and/or skin.Conductive materials used to form the feedline 110 may be plated withother materials, e.g., other conductive materials, such as gold orsilver, to improve their properties, e.g., to improve conductivity,decrease energy loss, etc. In some embodiments, the feedline 110includes stainless steel, and to improve the conductivity thereof, thestainless steel may be coated with a layer of a conductive material suchas copper or gold. Feedline 110 may include an inner conductor, adielectric material coaxially surrounding the inner conductor, and anouter conductor coaxially surrounding the dielectric material. Antennaassembly 12 may be formed from a portion of the inner conductor thatextends distal of the feedline 110 into the antenna assembly 12.Feedline 110 may be cooled by fluid, e.g., saline, water or othersuitable coolant fluid, to improve power handling, and may include astainless steel catheter.

In some embodiments, the power generating source 28 is configured toprovide microwave energy at an operational frequency from about 500 MHzto about 2500 MHz. In other embodiments, the power generating source 28is configured to provide microwave energy at an operational frequencyfrom about 500 MHz to about 10 GHz. Power generating source 28 may beconfigured to provide various frequencies of electromagnetic energy.Transmission line 15 may additionally, or alternatively, provide aconduit (not shown) configured to provide coolant fluid from a coolantsource 18 to one or more components of the probe 100.

Located at the distal end of the antenna assembly 12 is an end cap ortapered portion 120, which may terminate in a sharp tip 123 to allow forinsertion into tissue with minimal resistance. The end cap or taperedportion 120 may include other shapes, such as, for example, a tip 123that is rounded, flat, square, hexagonal, or cylindroconical.

In some variations, the antenna assembly 12 includes a distal radiatingportion 105 and a proximal radiating portion 140. A junction member 130may be provided. Junction member 130, or portions thereof, may bedisposed between the proximal and distal radiating portions, 140 and105, respectively. In some embodiments, the distal and proximalradiating portions 105, 140 align at the junction member 130, which isgenerally made of a dielectric material, e.g., adhesives, and are alsosupported by the inner conductor that extends at least partially throughthe distal radiating portion 105. Junction member 130 may be formed fromany suitable elastomeric or ceramic dielectric material by any suitableprocess. In some embodiments, the junction member 130 is formed byover-molding and includes a thermoplastic elastomer, such as, forexample, polyether block amide (e.g., PEBAX®, manufactured by The ArkemaGroup of Colombes, France), polyetherimide (e.g., ULTEM® and/or EXTEM®,manufactured by SABIC Innovative Plastics of Saudi Arabia) and/orpolyimide-based polymer (e.g., VESPEL®, manufactured by E. I. du Pont deNemours and Company of Wilmington, Del., United States). Junction member130 may be formed using any suitable over-molding compound by anysuitable process, and may include use of a ceramic substrate.

In some embodiments, the antenna assembly 12 may be provided with acoolant chamber (not shown). Additionally, the junction member 130 mayinclude coolant inflow and outflow ports (not shown) to facilitate theflow of coolant into, and out of, the coolant chamber. Examples ofcoolant chamber and coolant inflow and outflow port embodiments aredisclosed in commonly assigned U.S. patent application Ser. No.12/401,268 filed on Mar. 10, 2009, entitled “COOLED DIELECTRICALLYBUFFERED MICROWAVE DIPOLE ANTENNA”, and U.S. Pat. No. 7,311,703,entitled “DEVICES AND METHODS FOR COOLING MICROWAVE ANTENNAS”.

In some embodiments, the antenna assembly 12 may be provided with anouter jacket (not shown) disposed about the distal radiating portion105, the junction 130 and/or the proximal radiating portion 140. Theouter jacket may be formed of any suitable material, such as, forexample, polymeric or ceramic materials. The outer jacket may be appliedby any suitable method, such as, for example, heat shrinking,over-molding, coating, spraying dipping, powder coating, baking and/orfilm deposition. The outer jacket may be a water-cooled catheter formedof a material having low electrical conductivity.

During microwave ablation, e.g., using the electrosurgical system 10,the probe 100 is inserted into or placed adjacent to tissue andmicrowave energy is supplied thereto. Ultrasound or computed tomography(CT) guidance may be used to accurately guide the probe 100 into thearea of tissue to be treated. Probe 100 may be placed percutaneously orsurgically, e.g., using conventional surgical techniques by surgicalstaff. A clinician may pre-determine the length of time that microwaveenergy is to be applied. Application duration may depend on many factorssuch as tumor size and location and whether the tumor was a secondary orprimary cancer. The duration of microwave energy application using theprobe 100 may depend on the progress of the heat distribution within thetissue area that is to be destroyed and/or the surrounding tissue.Single or multiple probes 100 may provide ablations in short proceduretimes, e.g., a few minutes, to destroy cancerous cells in the targettissue region.

A plurality of probes 100 may be placed in variously-arrangedconfigurations to substantially simultaneously ablate a target tissueregion, making faster procedures possible. Multiple probes 100 can beused to synergistically create a large ablation or to ablate separatesites simultaneously. Tissue ablation size and geometry is influenced bya variety of factors, such as the energy applicator design, number ofenergy applicators used simultaneously, ablation time and wattage, andtissue characteristics.

In operation, microwave energy having a wavelength, lambda (λ), istransmitted through the antenna assembly 12, e.g., along the proximaland distal radiating portions 140, 105, and radiated into thesurrounding medium, e.g., tissue. The length of the antenna forefficient radiation may be dependent on the effective wavelengthλ_(off), which is dependent upon the dielectric properties of the mediumbeing radiated. Antenna assembly 12 through which microwave energy istransmitted at a wavelength λ may have differing effective wavelengthsλ_(eff) depending upon the surrounding medium, e.g., liver tissue asopposed to breast tissue.

Referring to FIGS. 2A and 4A, an embodiment of the antenna assembly 12of FIG. 1 (shown generally as 12A in FIG. 2A) includes an innerconductor 210, an outer conductor 260, and may include a firstdielectric material 240 separating the inner conductor 210 and the outerconductor 260. In some embodiments, the inner conductor 210 is formedfrom a first electrically-conductive material (e.g., stainless steel)and the outer conductor 260 is formed from a secondelectrically-conductive material (e.g., copper). In some embodiments,the outer conductor 260 coaxially surrounds the inner conductor 210along the proximal radiating portion 140, and may coaxially surround theinner conductor 210 along a distal portion of the antenna assembly 12A.Inner conductor 210 and the outer conductor 260 may be formed from anysuitable electrically-conductive material.

First dielectric material 240 may be formed from any suitable dielectricmaterial, including, but not limited to, ceramics, water, mica,polyethylene, polyethylene terephthalate, polyimide,polytetrafluoroethylene (a.k.a. PTFE or Teflon®, manufactured by E. I.du Pont de Nemours and Company of Wilmington, Del., United States),glass, metal oxides or other suitable insulator, and may be formed inany suitable manner. Antenna assembly 12A may be provided with a seconddielectric material 280 surrounding the outer conductor 260, or portionsthereof, and/or the junction member 130, or portions thereof. Seconddielectric material 280 may be formed from any suitable dielectricmaterial, and may have a thickness of about 0.001 inches to about 0.005inches. In some embodiments, the second dielectric material 280 isformed from a material with a dielectric constant different than thedielectric constant of the first dielectric material 240. In theembodiment shown in FIG. 2A, the antenna assembly 12A is provided with athird dielectric material 290 disposed proximal to the second dielectricmaterial 280 surrounding the outer conductor 260. Second dielectricmaterial 280 and the third dielectric material 290 may be formed of thesame material and/or may be formed in the same process.

Third dielectric material 290 may be formed from any suitable dielectricmaterial, and may be formed by any suitable process, e.g., over-moldingprocesses or heat shrinking. Third dielectric material 290 may be formedfrom a material with a dielectric constant different than the dielectricconstant of the second dielectric material 280 and/or the firstdielectric material 240. As shown in FIG. 2A, the third dielectricmaterial 290 may include a first segment 2901 and a second segment 2902disposed proximal to the first segment 2901. The shape and size of thefirst segment 2901 and the second segment 2902 may be varied from theconfiguration depicted in FIG. 2A.

In some embodiments, the antenna assembly 12A includes a conductor endportion 270, which may be formed from any suitableelectrically-conductive material. In some embodiments, the conductor endportion 270 is coupled to the inner conductor 210 and may be formed ofthe same material as the inner conductor 210. In some embodiments, theconductor end portion 270 may be spaced apart from the outer conductor260 by the junction member 130 disposed therebetween. Tapered region120, or portions thereof, may surround a portion of the conductor endportion 270. In some embodiments, the conductor end portion 270 issubstantially cylindrically shaped, and may be formed from stainlesssteel. The shape and size of the conductor end portion 270 may be variedfrom the configuration depicted in FIG. 2A. In some embodiments, atleast a portion of the conductor end portion 270 is surrounded by thesecond dielectric material 280.

Antenna assembly 12 of FIG. 1, according to various embodiments,includes a feed point (e.g., 350 shown in FIG. 2A) and a choke (e.g.,“C” shown in FIG. 2A) electrically coupleable to tissue, wherein thechoke is spaced apart from and disposed proximal to the feed point. Insome embodiments, the antenna assembly 12A may include a seconddielectric material 280 disposed around at least a portion of the distalportion of the outer conductor 260 and a third dielectric material 290disposed around at least a portion of the proximal portion of the outerconductor 260, wherein the third dielectric material 290 includes anopening (e.g., 291 shown in FIG. 4A) defined therein. In variousembodiments, the electrically-conductive member 295 is disposed in theopening 291 electrically coupled to the outer conductor 260 andconfigured to make contact with tissue (e.g., “T” shown in FIG. 6)during a procedure, e.g., an ablation procedure.

In the embodiment shown in cross-section in FIG. 2A, the choke “C”includes an electrically-conductive member 295 formed in a ring-likeshape concentrically disposed around the outer conductor 260 at aproximal end of a first segment 2901 of the third dielectric material290, having a length “L1”. A second segment 2902 of the third dielectricmaterial 290 may be disposed proximal to the electrically-conductivemember 295. Electrical current present in tissue around the choke “C”,according to embodiments of the present disclosure, may dissipaterelatively quickly where the operational frequency lies in certainfrequency bands, such as microwave, and electromagnetic radiation willgenerally be confined to the radiating portion of the antenna 12A.Electromagnetic radiation, if any, about the presently-disclosed choke“C”, or ohmic heating due to dissipated current present along the choke“C” area, may be useful for track-ablation.

In some embodiments, the second dielectric material 280 has a thicknessof about 0.001 inches to about 0.005 inches, and the first segment 2901of the third dielectric material 290 has a thickness of about 0.010inches, e.g., to improve electrical choke performance. The secondsegment 2902 may have a thickness different than the thickness of thefirst segment 2901. The shape and size of the opening 291 and theelectrically-conductive member 295 may be varied from the configurationdepicted in FIG. 2A.

FIGS. 2B and 3 show another embodiment of the antenna assembly 12 ofFIG. 1 (shown generally as 12B in FIG. 2B) in accordance with thepresent disclosure that is similar to the antenna assembly 12A of FIG.2A, except for the size, shape and/or location of the conductor endportion 270, the junction member 130, the second dielectric material 280and the electrically-conductive member 295, and the length of the distaland proximal radiating sections. As cooperatively shown in FIGS. 2A, 2Band 3, the distal end of the outer conductor 260 and the distal end ofthe first dielectric material 240 may be spaced apart by a gap (e.g.,“G” shown in FIG. 3) from the proximal end of the junction member 130 todefine a feed point 350 therebetween.

In the embodiment shown in FIG. 2A, the feed point 350 is disposed alength “L2” from the distal end of the antenna assembly 12A, and theelectrically-conductive member 295 is disposed a length “L1” from theproximal end of a proximal radiating section 140 defined by a length“L3”. In some embodiments, the length “L2” may be about one-halfwavelength, defining a distal radiating section 105, and the length “L3”may be about one-half wavelength, defining a proximal radiating section140. In some embodiments, the length “L1” is about one-quarterwavelength.

As shown in FIG. 2B, the feed point 350 may be disposed a length “L4”from the distal end of the antenna assembly 12B, and theelectrically-conductive member 295 may be disposed a length “L5” fromthe feed point 350. In some embodiments, the length “L4” may be aboutone-half wavelength, defining a distal radiating section 105, and thelength “L5” may be about one-half wavelength, defining a proximalradiating section 140.

Although the antenna assembly 12A shown in FIGS. 2A and 4A includes asingle, electrically-conductive member 295 positioned in the opening291, various combinations of different numbers ofelectrically-conductive members, variously sized and variously spacedapart from each other, may be provided to the antenna assembly 12A.Antenna assembly 12A, in accordance with embodiments of the presentdisclosure, may include a plurality of electrically-conductive membersthat are spaced apart from each other disposed in the third dielectricmaterial 290 and/or the second dielectric material 280, wherein eachelectrically-conductive member is electrically coupled to the outerconductor 260 and configured to make contact with tissue.

As shown in FIG. 4B, the electrically-conductive member 295 may includea protrusion portion 298 that protrudes outwardly relative to the outersurface “S” of the third dielectric material 290, e.g., to improve thecontact between the electrically-conductive member 295 and tissue.Protruding portion 298 may have various shapes, such as generallysemi-circular, bulbous, bowed, concave or convex shapes, and may besized to improve the electrical contact with tissue.

According to an embodiment of the present disclosure, an ablation probeshown generally as 500 in FIG. 5 includes an antenna assembly 512 havinga radiating portion 505 connected by a feedline 511 (or shaft) via atransmission line 15 to an energy source (e.g., 28 shown in FIG. 1).Antenna assembly 512 includes at least one substantiallyrectangular-shaped electrically-conductive member 595 configured to makecontact with tissue. Electrically-conductive member 595 is similar tothe electrically-conductive member 295 shown in FIG. 2A, except for itsshape, and further description thereof is omitted in the interests ofbrevity.

In the embodiment shown in FIG. 5, the ablation probe 500 includes anindicia alignment mark 510, e.g., a colored stripe, which is readilyvisible along the proximal end of the ablation probe 500. Indiciaalignment mark 510 is positioned such that the longitudinal axis of thealignment mark 510 substantially aligns with the longitudinal axis ofthe substantially rectangular-shaped electrically-conductive member 595,to provide a visual cue to the surgeon to allow orientation of theelectrically-conductive member 595 to coincide with the indiciaalignment mark 510. The visual assistance provided by the indiciaalignment mark 510, alone or in combination with the indicia graduationmarks 580, according to embodiments of the present disclosure, may allowthe surgeon to selectively position the electrically-conductive member595 in tissue. As shown in FIG. 5, one or more of the indicia graduationmarks 580 may overlap the indicia alignment mark 510. The shape and sizeof the indicia alignment mark 510 and the indicia graduation marks 580may be varied from the configurations depicted in FIG. 5. Antennaassembly 512 is similar to the antenna assembly 12A shown in FIGS. 2Aand 4A, except for the shape of the electrically-conductive member andthe indicia graduation marks 580 and the indicia alignment mark 510, andfurther description thereof is omitted in the interests of brevity.

FIG. 6 shows a diagrammatic representation of a radiation pattern “R” ofelectromagnetic energy delivered into tissue “T” by the ablation probe500 of FIG. 5. As shown in FIG. 6, the ablation probe 500 is coupled toa transmission line 15 that may further connect the ablation probe 500to a power generating source, e.g., a microwave or RF electrosurgicalgenerator. Ablation probe 500 may be placed percutaneously orsurgically. Ultrasound or computed tomography (CT) guidance may be usedto accurately guide the ablation probe 500 into the area of tissue “T”to be treated. The shape and size of the emitted radiation pattern “R”may be varied from the configuration depicted in FIG. 6.

FIG. 7 is a cross-sectional view of an embodiment of an electrosurgicaldevice 700 shown with a diagrammatic representation of an emittedradiation pattern in accordance with the present disclosure.Electrosurgical device 700 shown in FIG. 7 is similar to theelectrosurgical device 100 of FIGS. 1 and 2B through 4A and furtherdescription thereof is omitted in the interests of brevity.

FIGS. 8 and 9 are S-parameter (scattering parameter) magnitude graphsdisplaying magnitude in decibels (dB) with respect to frequency. Theillustrated results are based on simulations that modeled operation ofembodiments of an energy applicator provided with a choke in accordancewith the present disclosure. In FIG. 8, the graph shows a minimum atapproximately 1.05 GHz (˜−33 dB). The minimum plotted on the graph canbe interpreted as showing that the simulation generally modeled aresonant one-quarter wavelength antenna. The results illustrated in FIG.9, where the graph shows a minimum at approximately 915 MHz (˜−27 dB),were obtained by increasing the length of the radiating portion of theenergy applicator to match it to the desired 915 MHz, causing the energyapplicator to become resonant at one-half wavelength.

FIG. 10 is a flowchart illustrating a method of directing energy totissue according to an embodiment of the present disclosure. In step1010, an antenna assembly (e.g., 12 shown in FIG. 1) is positioned fordelivery of energy to tissue, wherein the antenna assembly includes aradiating portion (e.g., 105 shown in FIG. 2A), a feed point (e.g., 350shown in FIG. 3), and a choke (e.g., “C” shown in FIG. 2A) electricallycoupleable to tissue, the choke spaced apart from and disposed proximalto the feed point. The antenna assembly may be inserted directly intotissue (e.g., “T” shown in FIG. 6), inserted through a lumen, e.g., avein, needle or catheter, placed into the body during surgery by aclinician, or positioned in the body by other suitable methods. Theantenna assembly may be configured to operate with a directionalradiation pattern. In some embodiments, the radiating portion isconfigured for radiating energy in a broadside radiation pattern.

In step 1020, energy from an energy source (e.g., 28 shown in FIG. 1) istransmitted to the antenna assembly (e.g., 12 shown in FIG. 1). Forexample, the energy source may be any suitable electrosurgical generatorfor generating an output signal. In some embodiments, the energy sourceis a microwave energy source, and may be configured to provide microwaveenergy at an operational frequency from about 500 MHz to about 10 GHz.

In step 1030, the energy from the energy source is caused to radiatethrough the radiating portion to tissue while the choke is shorted totissue for blocking propagation of reflected energy towards the energysource.

The above-described electrosurgical devices for treating tissue andmethods of directing electromagnetic radiation to a target volume oftissue may be used to provide directional microwave ablation, whereinthe heating zone may be focused to one side of the electrosurgicaldevice, thereby allowing clinicians to target small and/or hard tumorswithout having to penetrate the tumor directly or kill more healthytissue than necessary. The presently disclosed electrosurgical devicesmay allow clinicians to avoid ablating critical structures, such aslarge vessels, healthy organs or vital membrane barriers, by placing theelectrosurgical device between the tumor and critical structure anddirecting the electromagnetic radiation toward the tumor and away fromthe sensitive structure.

Although embodiments have been described in detail with reference to theaccompanying drawings for the purpose of illustration and description,it is to be understood that the inventive processes and apparatus arenot to be construed as limited thereby. It will be apparent to those ofordinary skill in the art that various modifications to the foregoingembodiments may be made without departing from the scope of thedisclosure.

1. A device for directing energy to tissue, comprising: a feedlineincluding an inner conductor, an outer conductor and a first dielectricmaterial disposed therebetween; a radiating portion electrically coupledto the feedline, the radiating portion having a distal radiating sectionand a proximal radiating section; and a choke disposed around at least aportion of the feedline, the choke including: a second dielectricmaterial disposed around at least a portion of the outer conductor,wherein the second dielectric material includes at least one openingdefined therein; and an electrically-conductive member disposed in theat least one opening electrically coupled to the outer conductor,wherein the electrically-conductive member is configured to contacttissue.
 2. The device of claim 1, wherein the electrically-conductivemember is positioned about one-quarter of a wavelength from a proximalend of the proximal radiating section.
 3. The device of claim 2, whereinthe electrically-conductive member is formed in a ring-like shapeconcentrically disposed around the outer conductor.
 4. The device ofclaim 1, wherein the electrically-conductive member includes aprotrusion portion that protrudes outwardly relative to an outer surfaceof the second dielectric material.
 5. The device of claim 1, wherein theproximal radiating section includes at least a portion of the innerconductor and the first dielectric material and the distal radiatingsection includes a conductive element.
 6. An ablation probe forproviding energy to tissue, comprising: an inner conductor; an outerconductor coaxially surrounding the inner conductor, the outer conductorhaving a proximal portion and a distal portion; a first dielectricmaterial disposed between the inner conductor and the outer conductor; asecond dielectric material disposed around at least a portion of thedistal portion of the outer conductor; a third dielectric materialdisposed around the proximal portion of the outer conductor, wherein thethird dielectric material includes an opening defined therein; and anelectrically-conductive member disposed in the opening electricallycoupled to the proximal portion of the outer conductor, wherein theelectrically-conductive member is configured to contact tissue.
 7. Theablation probe of claim 6, further comprising: a feed point defined bythe inner conductor and the outer conductor; and a radiating portionelectrically coupled to the feed point at a point distal to the feedpoint.
 8. The ablation probe of claim 7, wherein the feed point ispositioned about one-half of a wavelength from a distal end of theradiating portion.
 9. The ablation probe of claim 7, wherein theelectrically-conductive member is positioned about one-half of awavelength from the feed point.
 10. The ablation probe of claim 6,wherein the electrically-conductive member is positioned aboutone-quarter of a wavelength from a proximal end of the proximalradiating section.
 11. The ablation probe of claim 6, wherein theelectrically-conductive member includes a protrusion portion thatprotrudes outwardly relative to an outer surface of the third dielectricmaterial.
 12. A method of directing energy to tissue, comprising thesteps of: positioning an antenna assembly for delivery of energy totissue, wherein the antenna assembly includes a radiating portion, afeed point, and a choke electrically coupleable to tissue, the chokespaced apart from and disposed proximal to the feed point; transmittingenergy from an energy source to the antenna assembly; and causing theenergy to radiate through the radiating portion to tissue while shortingthe choke to tissue for blocking propagation of reflected energy towardsthe energy source.